The development towards fault tolerant quantum computers has accelerated in recent years. It is therefore, reasonable to posit that quantum computers will be able to solve numerical problems previously unsolvable in a reasonable amount of time. This is particularly relevant in the context of factoring large composite numbers and solving the discrete logarithm problem. These two mathematical problems form the foundation for the vast majority of asymmetric encryption systems and key exchange procedures (such as RSA, DH, ECDH, ECDSA, and so forth). It is anticipated that quantum computers with cryptographic capabilities will become available within the next one or two decades. A significant number of high-security applications require the encryption of classified material beyond this timeframe. Consequently, the mitigation of the threats posed by quantum computers to classical encryption schemes has become a race against time, already. Currently two approaches are discussed to ensure quantum secure encryption and communications after the breakthrough of quantum computers. The first approach is called Post-Quantum-Cryptography (PQC). Here, new encryption and signature schemes are implemented based on mathematical problems which are hard to crack classically and by quantum computers. The second approach is based on a secure exchange of encryption keys and is referred to as Quantum Key Distribution (QKD). This approach utilizes the quantum mechanical properties of photons in a way that enables the sending and receiving parties to detect any attempts by an eavesdropper to record or alter the transmitted keys. If the successfully transferred keys are used only once for encryption unconditional security can be achieved in theory. Nevertheless, quantum key distribution (QKD) requires either dedicated fiber-optic lines that are solely used for the key exchange, commonly referred to as a dark fiber network or free-space links, which utilize a laser terminal and a telescope as the sender and receiver, respectively. Free-space links can be employed for mobile applications that facilitate quantum-secured communication with minimal deployment times over distances of several kilometers. Moreover, free-space links are utilized to exchange quantum keys between optical ground stations (OGS) and QKD satellites. By leveraging the in-orbit deployment of quantum keys, QKD enables the establishment of secure long- distance connections. DLR (Deutsches Luft- und Raumfahrtzentrum) is part of the Munich Quantum Network (MuQuaNet), which is a research dark fiber network situated in the metropolitan area of Munich. The project is spearheaded by the University of the Bundeswehr (Munich) and is operated in conjunction with a number of other research facilities and governmental institutions. The QKD network is comprised of multi-vendor QKD devices, including both prepare-and-measure and entanglement-based systems. DLR, in particular the German Space Operation Center (GSOC) assumed the task of demonstrating the use case of encrypting the ground segment for satellite operations employing QKD. This presentation will provide an overview of the current status of our work, including a technical explanation of the implementation and a general description of the approach used to encrypt part of our TMTC data streams as part of this QKD experiment.
The development towards fault tolerant quantum computers has accelerated in recent years. It is therefore, reasonable to posit that quantum computers will be able to solve numerical problems previously unsolvable in a reasonable amount of time. This is particularly relevant in the context of factoring large composite numbers and solving the discrete logarithm problem. These two mathematical problems form the foundation for the vast majority of asymmetric encryption systems and key exchange procedures (such as RSA, DH, ECDH, ECDSA, and so forth). It is anticipated that quantum computers with cryptographic capabilities will become available within the next one or two decades. A significant number of high-security applications require the encryption of classified material beyond this timeframe. Consequently, the mitigation of the threats posed by quantum computers to classical encryption schemes has become a race against time, already. Currently two approaches are discussed to ensure quantum secure encryption and communications after the breakthrough of quantum computers. The first approach is called Post-Quantum-Cryptography (PQC). Here, new encryption and signature schemes are implemented based on mathematical problems which are hard to crack classically and by quantum computers. The second approach is based on a secure exchange of encryption keys and is referred to as Quantum Key Distribution (QKD). This approach utilizes the quantum mechanical properties of photons in a way that enables the sending and receiving parties to detect any attempts by an eavesdropper to record or alter the transmitted keys. If the successfully transferred keys are used only once for encryption unconditional security can be achieved in theory. Nevertheless, quantum key distribution (QKD) requires either dedicated fiber-optic lines that are solely used for the key exchange, commonly referred to as a dark fiber network or free-space links, which utilize a laser terminal and a telescope as the sender and receiver, respectively. Free-space links can be employed for mobile applications that facilitate quantum-secured communication with minimal deployment times over distances of several kilometers. Moreover, free-space links are utilized to exchange quantum keys between optical ground stations (OGS) and QKD satellites. By leveraging the in-orbit deployment of quantum keys, QKD enables the establishment of secure long- distance connections. DLR (Deutsches Luft- und Raumfahrtzentrum) is part of the Munich Quantum Network (MuQuaNet), which is a research dark fiber network situated in the metropolitan area of Munich. The project is spearheaded by the University of the Bundeswehr (Munich) and is operated in conjunction with a number of other research facilities and governmental institutions. The QKD network is comprised of multi-vendor QKD devices, including both prepare-and-measure and entanglement-based systems. DLR, in particular the German Space Operation Center (GSOC) assumed the task of demonstrating the use case of encrypting the ground segment for satellite operations employing QKD. This presentation will provide an overview of the current status of our work, including a technical explanation of the implementation and a general description of the approach used to encrypt part of our TMTC data streams as part of this QKD experiment.
On the brink of the so-called quantum age, researchers from around the globe go to great lengths to better understand the quantum nature of light. Browne et al. (2017, p.1) state: 'Quantum light remains at the heart of many of the most promising and potentially transformative quantum technologies'. With the huge progress in quantum computing over the last years, quantum key distribution (QKD) is equally growing in importance. By exchanging secure keys using an optical link, QKD is able to solve security vulnerabilities arising through the insufficient protection of traditional encryption techniques against brute force quantum computer attacks threatening future communications. Pushing the limits of optical free space links for many years, the German Aerospace Center (DLR) has also gathered a lot of experience in QKD applications and is now aiming for a safe and powerful future optical communication network. As QKD networks become reality, optical freespace links ensure ground-satellite and satellite-satellite communication lines. Essential for ground-satellite links are accurate telescopes, which reduce satellite optics requirements due to their ability to gather light and focus collimated beams.
As digital communication continues to expand across critical infrastructures, ensuring data security has become more challenging in the face of advancing computational capabilities, especially with the anticipated rise of quantum computers. Quantum Key Distribution (QKD) presents a revolutionary approach to secure communications by leveraging the fundamental principles of quantum mechanics, such as superposition and entanglement, to enable the secure exchange of cryptographic keys. Unlike classical encryption methods that rely on computational complexity, QKD ensures unconditional security, as any attempt to intercept the key disturbs the quantum state, revealing the presence of eavesdroppers. This paper explores the current developments in QKD protocols, including BB84 and E91, as well as practical challenges in implementation, such as distance limitations and hardware requirements. Furthermore, it discusses recent advancements in satellite-based QKD, integrated photonics, and quantum networks, highlighting their potential to reshape the landscape of secure global communication. The integration of QKD into future communication infrastructure is positioned to be a cornerstone of post-quantum cryptography, making it a vital technology in the era of quantum computing.
Quantum key distribution (QKD), a novel cryptographic technique for secure distribution of secret keys between two parties, is the first successful quantum technology to emerge from quantum information science. The security of QKD is guaranteed by fundamental properties of quantum mechanical systems, unlike public-key cryptography whose security depends on difficult to solve mathematical problems such as factoring. Current terrestrial quantum links are limited to about 250 km. However, QKD could soon be deployed on a global scale over free-space links to an orbiting satellite used as a trusted node. \n \nEnvisioning a photonic uplink to a quantum receiver positioned on a low Earth orbit satellite, the Canadian Quantum Encryption and Science Satellite (QEYSSat) is a collaborative project involving Canadian universities, the Canadian Space Agency (CSA) and industry partners. This thesis presents some of the research conducted towards feasibility studies of the QEYSSat mission. \n \nOne of the main goals of this research is to develop technologies for data acquisition and processing required for a satellite-based QKD system. A working testbed system helps to establish firmly grounded estimates of the overall complexity, the computing resources necessary, and the bandwidth requirements of the classical communication channel. It can also serve as a good foundation for the design and development of a future payload computer onboard QEYSSat. \n \nThis thesis describes the design and implementation of a QKD post-processing system which aims to minimize the computing requirements at one side of the link, unlike most traditional implementations which assume symmetric computing resources at each end. The post-processing software features precise coincidence analysis, error correction based on low-density parity-check codes, privacy amplification employing Toeplitz hash functions, and a procedure for automated polarization alignment. \n \nThe system's hardware and software components integrate fully with a quantum optical apparatus used to demonstrate the feasibility of QKD with a satellite uplink. Detailed computing resource requirements and QKD results from the operation of the entire system at high-loss regimes are presented here.
Quantum Key Distribution (QKD) constitutes one of the most profound practical applications of quantum mechanics, enabling two parties to exchange cryptographic keys whose security is guaranteed by the fundamental laws of physics rather than the assumed computational hardness of mathematical problems. As quantum computing capabilities continue to advance, classical public-key infrastructure faces an existential threat, rendering QKD a critical component of post-quantum secure communication architectures. This paper presents a comprehensive survey of QKD spanning foundational protocols, rigorous security proofs, hardware implementation challenges, deployment experiences across metropolitan fiber networks, and recent satellite-based experiments. We analyze the BB84, E91, B92, SARG04, continuous-variable, measurement-device-independent (MDI-QKD), and twin-field (TF-QKD) protocols in depth, examining their security assumptions, achievable key rates, and practical limitations. Particular attention is given to side-channel vulnerabilities in realistic implementations, decoy-state methods for mitigating photon-number-splitting attacks, and finite-key security analysis. We review key performance benchmarks from commercial systems and discuss integration with classical network infrastructure. The paper concludes by identifying open challenges in quantum repeater development, satellite QKD scalability, and standardization efforts essential for large-scale deployment.
Recent advances in quantum computing and quantum information theory represent a severe threat to the current state of the art of data protection. In this context, new quantum-safe techniques have emerged in recent decades, which fall into post-quantum and unconditionally secure cryptographic schemes. The firsts rely on computational problems supposed to be hard also for quantum computers. In contrast, the seconds do not depend on the difficulty of a computational problem and are therefore immune to quantum power. In particular, unconditionally secure techniques include Quantum Key Distribution (QKD) protocols for transmitting secret keys thanks to the quantum properties of light. In this work, we discuss QKD networks and post-quantum algorithms, considering their opportunities and limitations and showing that reconciliation between these two directions of cryptography is feasible and necessary for the quantum era.This work is part of the activities of the PON project “Development of quantum systems and technologies for IT security in communication networks” (QUANCOM) which aims to the realization of a metropolitan quantum communication network through the collaboration between universities, research centers and companies operating in the communication market area.
Quantum key distribution (QKD) enables tap-proof exchange of cryptographic keys guaranteed by the very laws of physics. One of the last remaining roadblocks on the way towards widespread deployment of QKD is the high loss experienced during terrestrial distribution of photons, which limits the distance between the communicating parties. A viable solution to this problem is to avoid the terrestrial distribution of photons via optical fibers altogether and instead transmit them via satellite links, where the loss is dominated by diffraction instead of absorption and scattering. First dedicated satellite missions have demonstrated the feasibility of this approach, albeit with relatively low secure key rates. In order for QKD to become commercially viable, the design of future satellite missions must be focused on achieving higher key rates at lower system costs. Current satellite missions are already operating at almost optimal system parameters, which leaves little room for enhancing the key rates with currently deployed technology. Instead, fundamentally new techniques are required to drastically reduce the costs per secret bit shared between two distant parties. Entanglement-based protocols provide the highest level of security and offer several pathways for increasing the key rate by exploiting the underlying quantum correlations. In this contribution, we review the most relevant advances in entanglement-based QKD which are implementable over free-space links and thus enable distribution of secure keys from orbit. The development of satellite missions is notoriously lengthy. Possible candidates for a new generation of quantum payloads should therefore be scrutinized as early as possible in order to advance the development of quantum technologies for space applications.